This invention relates to injection molding and more particularly to an improved heated manifold member and a method of manufacturing the same.
The increasing use of injection molding to make a wide variety of products has led to its use to mold a greater variety of materials. However, some of the materials with the most desirable product properties have relatively critical narrow temperature ranges. Therefore, it has become even more desirable to be albe to maintain the melt at its optimum temperature throughout its flow through the hot runner passage.
In the past, manifold members or configurations having different heater arrangements have been used. For instance, it is known to locate cartridge or tubular heaters in a channel in the mainfold member with mechanical contact provided by wedging material around the heater or by cementing the heaters in with a heat transfer cement. However, these structures have the disadvantage that there is still considerable resistance to heat transfer across the materials and interfaces between the heating element and the manifold member body which has two unsatisfactory results. The first is that the application of heat to the melt flowing through the manifold member is not uniform so that it is not maintained at a constant predetermined temperature which has become more critical with the increasing use of materials which are more difficult to mold. The second is that in spots along the heating element where heat resistance is high due to inadequate construction, the temperature of the electrical resistance wire itself may rise to the point where it will burn out. These effects are amplified by the fact that temperature of the heating element must be maintained generally higher than it otherwise would be if improved heat transfer were provided across to the body of the manifold member. It is, or course, imperative that an entire operating system not be frequently shut down to replace a burnt out heating element and that the properties of the product not be deteriously effected by overheating of the material. Consequently, it has been found to be impossible or impractical to run certain types of material with this type of structure.